Production op aromatic hydrocarbons



Patented Mar. i9, 394% rnonuc'rrou or AROMATIC urnaocannons Joshua A. Tilton,

Baton Rouge, La... assignor to Standard Oil Development Company, a corpo=- ration of Delaware Application June 6, 1942, Serial No. 446,012

6 Claims. (Cl. 260-668) This invention relates to the production of substantially pure toluene from petroleum distillates and is more particularly concerned with certainimprovements in operation by means of which the yield of toluene obtained from said petroleum distillates may be materially increased.

It is known that petroleum distillates derived from certain crudes contain appreciable amounts of toluene and other aromatics such as xylenes. It is also known that fractions rich in aromatic hydrocarbons of various types can be obtained from such distillates by extraction with solvents such as liquid sulfur dioxide, phenol, furfural, nitrobenzene and the like which have preferential solvent power for aromatic hydrocarbons at temperatures at which they have relatively much lesssolvent power for paraffinic hydrocarbons. Aromatic hydrocarbon fractions obtained from petroleum distillates by solvent extraction meth ods however usually contain other hydrocarbons besides the aromatics. These are dissolved by the solvent along with the aromatics and it is difilcult, if not impossible, to segregate them by distillation because they have boiling points very,

close to those of the aromatics.

For many purposes for which a highly aromatic hydrocarbon oil is needed, for example in solvents, lacquers and high octane number motor fuels, aromatic extracts obtained by the solvent extraction of petroleum distillates are quite satisfactory and it is not particularly important converted to toluene and xylenes. Pump 2 withdraws petroleum distillate from tank [I through line 3 and forces it through line t into adistillation means 5. fraction boiling between about 200 and 350 F. is wlthdrawnthrough line 6 and collected in a tan l. Fractions boiling below 200 and above about whether the extract consists of a single aromatic hydrocarbon or a mixture of difierent aromatic hydrocarbons. 'For certain other purposes, however, for example, the nitration of toluene to produce TNT, it is essential to start with toluene of extremely high purity. Thus the U. S. Army specifications for nitration grade toluene require a purity of at least 99%.

It is a principal object of the present invention to provide a process by means of which it is possible to obtain greater yields of nitration grade toluene from petroleum distillates than have heretofore been obtainable.

The nature of the process and the manner in which it is carried out will be fully understood from the following description when read with reference to the accompanying drawings which are semi-diagrammatic views in sectional elevation of one type of apparatus-Which is suitable for the purpose.

Referring to the drawings numeral l designates a supply of petroleum distillate which may contain in addition to toluenes and xylenes certain naphthenic hydrocarbons which may be 350 F. are removed from distillation means 5 through lines 8 and 9 respectively. The fraction boiling between 200 and 350 F. collected in tank 7 will contain all of the toluene and xylenes present in the original petroleum distillate and in addition will contain any methylcyclohexane and dimethylcyclohexanes which may also have been present. Pump it withdraws the hydrocarbon fraction from tank 1 through line H and forces it through line l2 into and throughaheating means It. Tank it contains a supply of hydrogen. A compressor l5 withdraws hydrogen from tank It through line it and forces it through line H to a junction with line it. Therebya mixture of hydrogen and oil is formed which passes through the heating means it. Afterbeing heated in heating means it to a suitable reaction tern-=- perature, the mixture of oil and hydrogen-flows through line It into a reaction chamber ltwhich contains a catalytic material 2% the nature .of I

which willbe described in more detail below.

In reaction chamber 69 the hydrocarbon fraction is subjected to a high temperature and hi h pressure hydrogenation treatment. Ithas been found that the conventional destructive hydrogenation operation may be modified to cause substantial dehydrogenation simply by increasing the temperature of operation to substantially above that ordinarily employed. Thus, if any naphthenic hydrocarbons are present, these will be substantially converted in the high temperature hydrogenation operation to the corresponding aromatic hydrocarbons. For example, if methylcyclohexane and dimethylcyclohexanes are present, they will be converted to toluene and xylenes respectively. It is ordinarily found that in this operation more xylenes are produced than toluene. The ratio is usually of the order of one part toluene to one to two parts of 'xylenes. Cracking of acylic hydrocarbons which are less refractory than aromatics may occur in the reaction and, the cracked products may subse quently be hydrogenated. 1 v

Reaction chamber is is maintained under conditions which favor dehydrogenation of naphthenes. The temperature may be between 9 00 and 1150 F. and the pressure should be maintained between about 50 and 200'or more atmos- From distillation means 5 a pheres. The rate at which the hydrocarbon oil is fed through reaction chamber l9 may be between 1.0 and 4.0 volumes of total liquid per volume of catalyst per hour and the quantity of hydrogen which accompanies the oil through the reaction chamber could be between 1500 and 10,000 cubic feet per barrel of oil. The catalyst in reaction chamber i9 may consist of an oxide or sulfide of a metal of the VI group of the periodic system in admixture with smaller amounts of the oxides of zinc, magnesium or aluminum. Especially suitable catalysts comprise mixtures of magnesium oxide, zinc oxide and molybdenum oxide; mixtures of zinc oxide and chromium oxide and mixtures of tungsten sulfide and nickel sulfide.

Products of reaction leave reaction chamber i9 through line 2|, pass through a cooling means 22 and then discharge into a separating means 23 wherein gaseous and liquid products are separated under high pressure. The gaseous products which will consist essentially of hydrogen are removed from separating means 23 through line 24 and may be recycled to line ll by means of booster compressor 24a. The liquid products are removed from separating means 23 through line 25 and after passing through a pressure release valve 26 are collected in a low pressure separating means 21- from which gaseous products are removed through line 28 and may be passed to the refinery fuel line or otherwise disposed of. Liquid products now under low pressure are removed from separating means 21 through line 29 and introduced into a distillation means 30. From distillation means 30 a fraction boiling between 200 and 250 F. is removed through line 3| and collected in tank 32; This fraction will contain substantially all of the toluene which may have been present in the original narrow fraction segregated from the petroleum distillate and which may have been produced in reaction chamber l9. Fractions boiling above about 250 F. are removed from distillation means 30 through line 33 and are recy- 'cled to tank I by means of pump 34. In the event that these fractions contain substantial quantities of non-aromatic hydrocarbons,-it may be desirable to subject them to a solvent extraction treatment and then recycle only the extract to tank I. In this way an accumulation of nonaromatic material in the system may be prevented. These fractions boiling above 250' F. will contain any xylenes originally present in the petroleum distillate and any which may have been produced in reaction chamber 19 and may also contain some polymers which may be removed by distillation if desired. By recycling these xyienes through the high temperature hydrogenation operation it is found that a considerable proportion thereof may be converted to toluene. Thus it will be seen that a toluene fraction is continuously removed from the products of the high temperature hydrogenation operation while the fractions boiling above toluene are continuously recycled to the high temperature hydrogenation operation wherein they are eventually converted to toluene.

The toluene containing fraction collected in tank 32 is removed therefrom through line 35 icy-means of pump 36 and forced through line 31. ,.It is then subjected to either one of two types of solvent extraction for the recovery therefromof substantially pure toluene. One type of solvent extraction may be designated liquid-liquid extraction and the other type may be des ignated liquid-vapor extraction.

If the liquid-liquid type extraction is to be used, a hydrocarbon fraction flowing through line 31 is passed through line 38 into the upper portion of a conventional solvent extraction tower 39. The hydrocarbon is mixed with several volumes of a suitable selective solvent suchas liquid sulfur dioxide which is supplied to line '38 from tank 40 through line 41. In extraction tower 39 the mixture of liquid S02 and hydrocarbon is countercurrently washed with a non-aromatic hydrocarbon diluent which is supplied from tank 42 through line 43, pump 44 and line 45 to the bottom portion of tower 39. The extraction tower 39 is preferably maintained at a low temperature,.say between about 20 and F. The

non-aromatic hydrocarbon diluent is preferably precooled to a temperature between 20 and -60 F. prior to its introduction into the tower but may be supplied at atmospheric temperature if other means are provided for cooling the tower. The non-aromatic hydrocarbon diluent supplied from tank 42 should be a highly parafiinic hydrocarbon oil having a boiling range substantially different from those of the liquid sulfur dioxide and the toluene and other hydrocarbons'present in the hydrocarbon fraction. The diluent may have a boiling range either higher or lower than the hydrocarbons in the hydrocarbon fraction. Examples of a suitable lower boiling diluent are pentane or isopentane. Examples of a higher boiling diluent are a parafiinic solvent naphtha and a light kerosene;

In the event that the fraction boiling between 200 and 250 F. collected in tank 32 contains a substantial proportion of non-aromatic hydrocarbons, it may be preferable to subject this fraction to a preliminary extraction with liquid S0: in order to segregate the aromatics from the bulk of the non-aromatic hydrocarbons. If this procedure is adopted, the solvent extraction phase from the preliminary extraction will be introhydrocarbon diluent with which the mixture of hydrocarbon and liquid S02 is countercurrently washed is what may be called "dilution displacement. This may be explained as follows:

The hydrocarbon fraction will contain, in addition to toluene and possibly other aromatics, a smaller amount of non-aromatic hydrocarbons which boil in the same range as toluene and said other aromatics and which therefore can not be separated therefrom by distillation or fractionation. By countercurrently washing the mixture of liquid S02 and hydrocarbon fraction with a relatively large volume of a non-aromatic hydrocarbon oil having a. boiling range widely different from that of any of the constituents in the hydrocarbon fraction, the concentration of the non-aromatic hydrocarbons originally associated with th hydrocarbon fraction is greatly diluted and these non-aromatic hydrocarbons are reany other constituents of said extract phase.

Having ssentially replaced the non-aromatic hydrocarbons originally associated with the hydrocarbon fraction which boil in the same range 2,896,761 as toluene with non-aromatichydrocarbons having a much diflerent boiling range, it is now possible to separate the non-aromatics from .-the toluene by ordinary fractionation.

For purposes of description it will be assumed that the non-aromatic hydrocarbon diluent supplied from tank 42 is a paramnic hydrocarbon oil boiling between about 350 and 400 F. or higher.

The volume of non-aromatic hydrocarbon diluent with which the mixture of liquid S02 and hydrocarbon fraction is countercurrently washed should be at least sufficientto efiect a substantial dilution displacement and maybe from about 50 to about 150% or more of the volum of the mixture of liquid S02 and hydrocarbonfraction. The volume of non-aromatic hydrocarbon diluent should not however be so great asto displace the liquid $02 from the hydrocarbon fraction.

A rallinate phase which will consist chiefly of non-aromatic hydrocarbon diluent, non-aromatic hydrocarbons, and possibly some liquid S02 is removed from extraction tower 39 through line it. It will be understood that the liquid S02 and nonaromatic hydrocarbon diluent may be recovered from this raflinate phase and reused in the extraction. It will also be understood that any toluene which may be present in the rafiinate removed from the top of tower 39 may be recovered by recycling said railinate to the top of towe 39.

An extract phase is removed from the bottom of extract tower 39 through line 41 and introduced into a distillation means 83. This extract phase will contain most of the sulfur dioxide and aromatic hydrocarbons present in tower 39 and in addition will contain a small quantity of nonfor countercurrent flow of liquid and vapors. Numeral designates a supply of a selective solvent having 'a boiling point substantially above the boiling range of the hydrocarbons to be extracted, 1. e. in the present case above about 250 F. This solventshould be one which is characterized by its ability to reduce the vapor pressure of aromatic hydrocarbons to a substantial extent while at the same timereducing the vapor pressure of other types of hydrocarbons to a muchsmaller extent. Examples of suitable solvents of this type are phenol, cresol, cresylic acid, mixtures of phenol and cresylic acid, furfural, aniline and beta-beta dichlorethyl ether. Phenol is a particularly (suitable solvent.

Solvent is removed from tank M through line 7 l5 and introduced into the upper portion of tower 13 wherein it remains in liquid phase and flows downwardly countercurrent to the upwardly rising hydrocarbon vapors. The quantity of solvent used may be between 50 and 1ooo% of the liquid volume of the hydrocarbons to be extracted. It will be understood that extraction tower 13 is maintained by suitable means at a temperature above the vaporizing temperature of the hydrocarbons but below the vaporizing temperature of the solvent.

means 38 through line and returned to the diluent supply tank 62. The remainder of the extract phase i withdrawn from distillation means d8 through line 5! and is then subjected in an apparatus designated by numeral 52 to a treatment with sulfuric acid to remove olefinic and unsaturated naphthenic hydrocarbons. Acid sludge may be removed from apparatus 52 through line 53. The acid-treated extract, after neutralization, is removed from apparatus 52 through line 543 and introduced into a fractionating means 55. Substantially pure toluene is removed from fractionating means 55 through line 56 and collected in a tank bl. Fraction boiling below and above toluene are removed from fractionating means 55 through lines 58 and 59 respectively. It will be understood that these fractions may be recycled to the extraction system in order to recover any toluene Which they may contain.

In the event that the fraction boiling between 200 and 250 F. which is collected in tank 32 has a high olefin content, it may be preferable to subject this fraction to treatment with sulfuric'acid prior to the extraction because olefins react with sulfur dioxide at high temperatures and this would tend to cause fouling of the heaters in the distillation and stripping means. v

If the liquid-vapor type of extraction is to be used, the toluene containing fraction flowing through line 31 is passed through line It into and through a heating means it wherein it is heated to a temperature somewhat above its vaporizing" temperature and the vapors are then introduced through line l2 into the middle portion of a conventional extraction tower 73 which i adapted naphthenic hydrocarbons.

Vapors substantially free from aromatic hydrocarbons are removed from extraction tower it through line it. Aromatic hydrocarbons dissolved in the selective solvent are removed from the bottom of extraction tower l3 through line ill and introduced into a distillation means it. Solvent is removed from distillation mean it through line it and may be returned to solvent supply tank it. Vapors of toluene together with those of any other aromatic hydrocarbons which may be pres out are removed from distillation means it .through line all, passed through a cooling means 8i and then, if necessary, subjected to acid treatment in an apparatus designated by the numeral 82 in order to remove olefins and unsaturated Acid sludge may be removed from apparatus 8% through line 83. The acidtreated extract is removed from apparatus 82 through line 8d and introduced into a fractionating means ad from which substantially pure toluene is removed through line as and then collected in a. tank 8i; Fractions boiling below and above toluene are removed from fractionating means as through lines 88 and d9 respcctivelys in the case of the liquid-liquid extraction,.the

fractions boiling below and abov toluene may be recycled to extraction tower is in orde to insure that all the toluene will be recovered therefrom.

While the process has been described with particular reference to the treatment of a fraction boiling between 200 and 350 F. which will contain methylcyclohexane and dimethylcyclohexanes it should be understood that the process is also applicable to the treatment of higher boiling naphthenic hydrocarbons, say, for example, those contained in fractions boiling up to about 450 F.

In carrying out the process many variations in v the operating details may be made without dethe apparatus may be made as are customary in the art.

gating from petroleum a fraction boiling between 200 and 350 F., subjecting this fraction to treatment with hydrogen at high temperature and high pressure, under which conditions dehydrogenation of naphthenes occurs, segregating from the products of hydrogenation a fraction boiling between 200 and 250 F. and a fraction rich in xylenes boiling above 250 F., recycling this latter fraction to the high temperature hydrogenation, extracting the fraction boiling between 200 and 250 F. with a solvent which is selective for aromatic hydrocarbons, treating the solvent extract with sulfuric acidto remove olefins and unsaturated naphthenic hydrocarbons, and fractionating the acid-treated extract to obtain substantially pure toluene.

2. Process according to claim 1 in which the hydrogenation is carried out at a temperature between 900 and 1150 F., under a pressure in excess of 50 atmospheres and in the presence of a catalyst comprising a major proportion of an oxide of a metal of the VI group of the periodic system.

3. Process according to claim 1 in which the fraction boiling between 200 and 250 F. segre- 35 gated from the products of hydrogenation is extracted with liquid sulfur dioxide at a temperaxylenes boiling above 250 F., subjecting the fraction boiling between 200 and 250 F. to extraction in vapor phase with phenol which remains in liquid phase at the temperature of extraction, removing the phenol from the extract phase, treating the extract with sulfuric acid to remove unsaturated hydrocarbons, and fractiohating the acid-treated extract to obtain toluene of at least 99% purity.

6. An improved process for obtaining high yields of toluene of at least 99% purity from petroleum distillate containing naphthenic hydrocarbons which comprises segregating from said distillate a fraction boiling between 200 and 350 F., subjecting this fraction to treatment ture between -20 and -60 F. and the extract phase is countercurrently washed with a nonaromatic hydrocarbondiluent having a boiling 40 hydrogated from the products of hydrogenation is countercurrently extracted in vapor phase with a selective solvent which remains in liquid phase at the temperature of extraction.

with hydrogen at a temperature between 900 and 1150 F. under a pressure above atmospheres in the presence of a catalyst comprising a mixture of magnesium oxide, zinc oxide and molybdenum oxide, segregating from the product of this treatment a fraction boiling between 200 and 250 F., continuously recycling to the hydrogen treatment fractions of the product, rich in xylenes, boiling above 250 F., subjectin the fraction between 200 and 250 F. to extraction in vapor phase with phenol which remains in liquid phase atthe temperature of extraction, removing the phenol from the extract phase, treating the extract with sulfuric acid to remove unsaturated hydrocarbons and fractionating the acid-treated extract to obtain toluene of at least 99% purity.

JOSHUA A. TILTON. 

